Spontaneous autophosphorylation of Lyn tyrosine kinase at both its activation segment and C-terminal tail confers altered substrate specificity.
Two tyrosyl residues have been reported to play a crucial role in the regulation of protein tyrosine kinases of the Src family: autophosphorylation of Tyr416 (c-Src numbering) located in the catalytic domain correlates with enzyme activation, while Csk-mediated phosphorylation of the C-terminal tyrosine Tyr527 (c-Src numbering) gives rise to inactive forms of Src kinases. Here we show that the Src-related Lyn kinase undergoes spontaneous and stoichiometric autophosphorylation at both Tyr396 (homologous to c-Src Tyr416) and Tyr507 (homologous to c-Src Tyr527). Such a doubly autophosphorylated form of Lyn is hyperactive toward peptide substrates and insensitive to Csk-induced downregulation. In contrast, doubly autophosphorylated Lyn exhibits reduced activity toward protein substrates such as phospho-p50/HS1 (hematopoietic-lineage cell-specific protein) and p57/PDI (protein disulfide isomerase related protein), whose multiple sequential/processive phosphorylation relies on the accessibility of the SH2 domain of the kinase. These data disclose a novel conformation of Lyn that is catalytically active despite the presence of an intramolecular interaction between the phosphorylated tail and the SH2 domain. This enzyme conformation is expected to display a reduced oncogenic potential resulting from its defective recognition of a subset of protein substrates whose targeting is mediated by the Lyn SH2 domain.
Donella-Deana
A
A
Dipartimento di Chimica Biologica, University of Padova, Italy. arianna@ck2.bio.unipd.it
Cesaro
L
L
Ruzzene
M
M
Brunati
A M
AM
Marin
O
O
Pinna
L A
LA
D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D000081247:CSK Tyrosine-Protein Kinase; D015536:Down-Regulation; D004789:Enzyme Activation / Q000187:drug effects; D008969:Molecular Sequence Data; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000494:pharmacology; D051381:Rats; D013379:Substrate Specificity; D014443:Tyrosine / Q000378:metabolism; D019061:src-Family Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*
D014443:Tyrosine; D011505:Protein-Tyrosine Kinases; D000081247:CSK Tyrosine-Protein Kinase; C060902:lyn protein-tyrosine kinase; D019061:src-Family Kinases